1. Field of the Invention
The present invention generally relates to heaters on which heating-subject articles are loaded to undergo heat processes. More specifically, the present invention relates to heaters that can be advantageously used in semiconductor manufacturing equipment, where they are especially used for heat-treating semiconductor wafers.
2. Description of the Related Art
In the fabrication of electronic circuits and displays, semiconductor, dielectric, and electrically conducting materials are formed on a substrate, such as for example, a semiconductor wafer, ceramic or glass substrate. The materials are formed for example, by chemical vapor deposition (CVD), physical vapor deposition (PVD), ion implantation, oxidation, nitridation and other such processes. Thereafter, the deposited substrate materials can be etched to form features such as gates, vias, contact holes and interconnect lines. These processes are typically carried out in a process chamber, as for example described in U.S. Pat. No. 6,491,978, to Kalyanam et al. In such processes, the substrate is placed on a substrate support and exposed to a process zone in the chamber. The support often includes a heater to further regulate the temperatures of the substrate during processing.
The heat generation of the heater is directly related to the electrode properties and geometry. In a layered heater structure where a thin layer of electrode is placed on an insulating substrate, the electrode resistivity and thickness play critical roles in achieving a desired temperature profile at the heater surface. For most of the wafer processes, a uniform thermal profile with less than 1% variation is required. An even tighter temperature range for the repeatability of heater products is desirable. The applicants are not aware of any known film deposition technique demonstrating a synthesis of electrode layer meeting the uniformity requirements, both in electrical properties and thicknesses.
In general, a small variation of a few percent in the electrode resistivity or thickness will cause a noticeable temperature offset on the heater surface. A common electrode characterizing method uses a four-point probe measurement to map the sheet resistance profile across the electrode. The typical resolution of the four-point probe measurement gage is 10−3 Ohm/sq and less. Such a resolution makes the gage incapable of capturing the resistance variation when the electrode layer has a sheet resistance of 10−2 Ohm/sq and less. Other electrode characterization methods, such as the use of resistance meters, also have a resolution limitation. Another drawback of using resistance meters is the contact resistance between the electrical probes and the electrode surface, which contribute a large portion of the measurement variation. For an electrode layer with a total resistance of 10 Ohm, an acceptable electrode characterization gage needs to have a resolution of 10−3 Ohm or less in resistance and 25 um in space and to be independent of the contact resistance. The applicants are not aware of any existing gage system that meets these requirements.
In addition, there is no precise technique of tuning the electrode to the right resistivity or thickness even if the characterization method were not an issue. Since the heater local temperature is very sensitive to the local sheet resistance of the electrode layer, thickness trimming practices, such as grinding or blasting, and resistivity adjustment, such as local heat treat, are very aggressive and uncontrollable which does not make them suitable for precisely tuning the electrode resistance within a few percent. A drawback of these practices is that they are typically very labor intense and time consuming.